As set forth in U.S. Patent Application Publication No. 2005/0240229, which is incorporated herein by reference, a large number of men suffer erectile dysfunction to a greater or lesser degree. Erectile dysfunction etiologies include neuropathy and vascular disease. The male erectile response is initiated by the action of neurons, or nerve cells (i.e., neuronal action), and is maintained by a complex interplay between events involving blood vessels (i.e., vascular events) and events involving the nervous system (i.e., neurological events).
Male erectile dysfunction has a number of causes, both physiological and psychological, and in many patients the disorder may be multifactorial. Several causes are essentially neurologic in origin. Damage to the spinal cord may produce varying degrees of erectile failure depending on the location and severity of the damage. Damage to the pathways used by the autonomic nervous system to innervate the penis may interrupt psychogenic erection initiated by the central nervous system. Damage to somatic nervous pathways may impair reflexogenic erections and may interrupt tactile sensation needed to maintain psychogenic erections. Not only do traumatic lesions affect erectile ability, but also disorders leading to peripheral neuropathy may impair neuronal innervation of the penis or of the sensory afferents. The endocrine system itself, particularly the production of androgens, appears to play a role in regulating sexual interest, and may also play a role in erectile function. Erectile dysfunction is also a common complication of prostate surgery, such as prostatectomy (surgical removal of all or part of the prostate), which is a mainstay of treatment for prostate cancer.
The oral antipressor agent, sildenafil citrate (available from Pfizer, Inc. of New York, N.Y., under the trademark VIAGRA), is clinically available for treatment of male erectile dysfunction. An oral dose typically requires an hour to achieve full effect. The agent may have side effects such as abnormal vision, flushing, headache, and diarrhea, however, the ability to preserve erectile function following prostate surgery has been favorably affected by the availability of sildenafil. Sildenafil appears to be most effective when there is some remaining erectile function.
In intracavernosal injection therapy, the patient injects vasodilator agents (e.g., alprostadil, papaverine, phentolamine) directly into the corpora of the penis, thus avoiding undesirable systemic effects of the agent. The most commonly used drug is alprostadil, a naturally occurring prostaglandin, which is present in the penis and is involved in the natural erection process. Alprostadil relaxes the blood vessels and muscles in the erectile tissue of the penis allowing increased blood flow, the basis of a normal erection. However, a high rate of patient dropout occurs due to the unpleasant delivery mode.
Erectile dysfunction may also be treated transcutaneously at a site of concern using prostaglandins such as PGE or alprostadil, nitroglycerin, papaverine, yohimbine, sildenafil citrate, apomorphine HCI, and other known agents.
Implantable drug delivery pumps have been described for implantation in the scrotum or subcutaneously in the abdominal region. Such pumps store a vasoactive agent (e.g., a vasodilator), and provide a mechanism for delivering a bolus of the stored agent into the corpus cavernosum. See, for example, the description of various implantable drug pumps set forth in U.S. Pat. No. 6,679,832′, which is incorporated herein by reference, and references cited therein. Generally, such implantable drug pumps comprise a refillable fluid agent storage chamber, a pump mechanism for delivering the bolus of agent from the storage chamber, and a catheter extending from the pump mechanism to deliver the agent to the site in the corpus cavernosum. The pump mechanism may be manually actuated by the patient to deliver a bolus of vasoactive agent.
As noted in U.S. Pat. No. 5,328,460, which is incorporated herein by reference, implanting a pump in a patient may trigger tissue growth encapsulating substantially the entire distal end of the catheter and blocking the lumen end opening or intruding into and thereby blocking or occluding the catheter lumen and inhibiting the delivery of medication. A mechanism for detecting such obstructions is proposed in the U.S. Pat. No. 5,328,460 patent.